The present invention relates to making a three-dimensional part or volume that presents a face in the form of a surface of revolution and that has a structure that is made up of a plurality of cavities separated by walls of small thickness. The invention relates more particularly to machining structures made up of thin-walled hollow bodies in order to make such parts.
The fabrication of such parts, such as for example packing structures for fluid exchange columns, comprises making a structure or a block made up of an assembly of thin-walled hollow bodies (e.g. tubes, honeycomb cells, etc.) and then machining the block to the shape and dimensions required for the final part.
Nevertheless, machining a structure of that type is problematic. Because of the small thickness of the walls, traditional machining tools such as grindwheels or the like are not suitable. The cutting force produced by such tools is too great and leads to the walls being deformed and/or destroyed, thereby preventing the final part from being shaped.
A jet of water under pressure can provide a solution to this problem, since it enables direct contact with the material under attack to be avoided and therefore does not generate a cutting force thereon. Nevertheless, a water jet is mainly used as a tool for cutting solid materials and not hollow bodies. It is known that using a water jet to cut a hollow body is very imprecise and leads to the appearance of large amounts of taper and flash. FIG. 1 shows a structure 10 made up of two juxtaposed tubes 11 and 12 being cut by means of a water jet. The structure is cut by delivering a water jet 2 at high speed from a nozzle 1, the jet initially striking the top portion 12a of the wall of tube 12. It can be seen that the jet is deflected and diverges after passing through the top portion 12a of the wall of the tube 12. Where the following wall, i.e. the bottom portion 12b of the tube 12 will be attacked then becomes imprecise both concerning the position of the cutting and the size thereof. This lack of precision in attack becomes worse as the water jet encounters successive walls, here the top and bottom portions 11a and 11b of the wall of the tube 11.
As can be seen in FIG. 1, when machining structures made up of thin-walled cavities, each wall that has been passed through acts as a diaphragm for the applied water jet, such that it is impossible to obtain a precise line of cut over all of the successive walls that are to be cut. The direction and the line of cut with a water jet can be under control only when cutting solid materials. In addition, when using a water jet to cut a hollow body, the divergence of the jet leads to it losing energy. The cutting force of the jet can then be insufficient for attacking the following walls, thereby leading to the structure under attack being cut incompletely.
Another solution for machining structures made up of hollow bodies consists in using cutter tools at very high speed. Nevertheless, that type of tool is used essentially for precision machining over small dimensions. Use thereof is not appropriate for machining bodies of revolution of relatively large dimensions, in particular because of the costs involved with that type of tool (frequent replacement of the cutter tools is required).